Imagine you are taking a walk in the forest. The forest is a public place (where I live anyway!) – anyone can walk anywhere they want. Eventually, later in the day, you might need to take a leak, so you do what everyone normally does – go behind a tree.
Do you in this situation expect to be photographed and have high-resolution pictures of your genitals posted to Instagram? Don't you think this, if it were a regular occurrence, would interfere with people's age-old custom of enjoying a quiet walk in the public forest?
Taking pictures of someone specifically may be different because that may be harassment.
But in general ending up in pictures and films of others because you were in a public space fits in the standard concept of what a public space is.